The North Atlantic Subpolar Ocean Dynamics during the Past 21,000 Years

Numerous studies have suggested that the North Atlantic subpolar gyre (SPG), Atlantic Meridional Overturning Circulation (AMOC), and Arctic sea ice impact the polar and global climate. Here, we use a fully linked atmosphere-ocean-sea ice Earth system model to investigate the North Atlantic subpolar ocean dynamics over the last 21 thousand years before the present (ka). We found that the SPG strength, net ocean surface heat flux, and mixed layer depth in the North Atlantic deep convection sites declined during the Heinrich 1 (H1; ∼19–17 ka) and Younger Dryas (YD; ∼12.9–11.3 ka) cold events. Consequently, the deep convection and AMOC strength declined, reducing the northward meridional heat transport and causing the expansion of Atlantic sea ice coverage. We also found that the North Atlantic subpolar net ocean surface heat flux varied coherently with AMOC strength throughout the past 21 ka. Subsequently, we observed a sea ice-capping mechanism wherein an increase (decrease) in Atlantic sea ice coverage during H1/YD (Bølling-Allerød (BA; 17–14.35 ka)) reduces (increases) net ocean surface heat flux and deep convection, thereby influencing the AMOC strength. Meanwhile, the SPG and AMOC strengths have been in-phase throughout the past 21 ka, except during the abrupt termination and input of freshwater flux during the BA and Meltwater Pulse 1 A (∼14.4–13.9 ka) events, respectively. In conclusion, our study suggests that a sudden shift in freshwater discharge into the subpolar North Atlantic may disturb the polar ocean dynamics.